ineteen letters from Romsey’s Lord Mountbatten to a former naval comrade turned inventor are up for auction in Sotheby’s in London next Tuesday (December 9).

The collection of quite revealing personal letters are from Lord Louis to Arthur Cotton, many concerning Mountbatten’s involvement in Cotton's inventions and particularly the company “Repeating Gramophones Limited .

Arthur Cotton was an old Etonian, Cambridge graduate, friend and brother officer of “Dickie” Mountbatten, in the Royal Navy.

Lord Louis used his royal connections to promote Cotton’s products and in one letter writes: “The gramophone is a great success & H.R.H. is delighted with it. He was so pleased with it that he always used to bring visitors up to it and ask them if it wasn't the neatest thing they had ever seen...”

Mountbatten also tried to help his friend’s business by sending him a letter of introduction to composer Jerome Kern, A later letter explains Mountbatten’s decision to resign as a company director and others concern his continued investment in Cotton’s troubled company.

Another advises Cotton on his love life: “Perhaps it is best to be absolutely faithful and always at her beck & call. If that doesn’t work you can always pretend to have an affair with someone else...”

Relationships became strained between the two – perhaps due to Cotton’s failing business and there is a break in correspondence from 1925 to 1938.

Later correspondence is of a more formal nature and is often typed.

The collection is expected to sell for between £2,000 and £2,500.